The syntheses of mitochondria in cells requires the close cooperation of two genetic systems: The majority of mitochondrial proteins are specified by nuclear genes and made on cell-sap ribosomes, just like other proteins in the cell. A minority of the mitochondrial proteins is specified by a second genetic system which resides in the mitochondria itself. This system consists of mitochondrial DNA and all the enzymes required to make RNA and translate these RNAs into protein. Our knowledge of this system has made tremendous advances in the last three years. By genetic approaches most of the genes in yeast mitochondrial DNA have been identified and the way their expression is controlled by nuclear genes is rapidly being unravelled. The complete 15,000 base pair sequence of human mitochondrial DNA and large parts of the sequence of the 5-fold larger yeast mitochondrial DNA have been determined. This has led to the discovery that fundamental aspects of the mitochondrial genetic system are very different from these of all other genetic systems: tRNAs, ribosomes and even the genetic code are highly unusual. The recent finding of intervening sequences (introns) has provided new tools for the study of RNA processing. Discovery of various types of mutations localized inside of introns has revealed novel functions of these sequences and brought new ideas about the regulation of gene expression. Thus mitochondrial genes and mitochondrial biogeneses are in the center of current research on gene organization and expression in higher organism. The objective of the meeting on "Mitochondrial Genes" is to bring together the leading molecular biologists who study genetics and biochemistry of mitochondrial biogeneses to obtain an up-to-date overview of the overwhelming mass of new data that are rapidly accumulating. The meeting should foster an intensive exchange of ideas and results between research workers studying mitochondrial genes in yeasts, plants, and protozoa and coming from different parts of the world.